The present invention relates generally to fuel injection systems for internal combustion engines, and more specifically to techniques for estimating pilot and/or post-injected fuel quantities and minimizing variations between such fuel quantities.
In recent years, advances in fuel systems for internal combustion engines, and particularly for diesel engines, have increased dramatically. However, in order to achieve optimal engine performance at all operating conditions with respect to fuel economy, exhaust emissions, noise, transient response, and the like, further advances are necessary. As one example, operational accuracy with electronically controlled fuel systems can be improved by reducing variations in injected fuel quantities.
A number of techniques are known for reducing injected fuel quantity variations such as, for example, robust system design, precision manufacturing, precise component matching, and electronic control strategies. However, conventional manufacturing approaches for improving performance, such as tightening tolerances and the like, are typically cost prohibitive, and conventional control approaches such as open-loop look-up tables have become increasingly complex and difficult to implement as the number of degrees of freedom to control have increased, particularly with multiple-input, multiple-output (MIMO) control systems. In fact, both of these approaches improve accuracy only during engine operation immediately after calibration in a controlled environment, and neither compensate for deterioration or environmental noise changes, which affect subsequent performance. Closed-loop control systems for controlling injected fuel quantity variations are accordingly preferable, but typically require additional sensors to measure appropriate control parameters.
One known technique for implementing such a closed-loop control system without implementing additional sensors is to leverage existing information to estimate injected fuel quantity; i.e., implementation of a so-called xe2x80x9cvirtual sensor.xe2x80x9d One example of a known control system 10 including such a virtual sensor is illustrated in FIG. 3. Referring to FIG. 3, system 10 includes a two-dimensional look-up table 14 receiving an engine speed/position signal via signal line 12 and a desired fuel injection quantity value from process block 16 via signal path 18. Table 14 is responsive to the engine speed/position signal and the desired fuel injection quantity value to produce an initial fueling command as is known in the art. The virtual injected fuel quantity sensor in system 10 typically comprises a two-dimensional look-up table 20 receiving the engine speed/position signal via signal path 12 and a fuel pressure signal from signal path 22. Table 20 is responsive to the fuel pressure and engine speed/position signals to produce an injected fuel quantity estimate that is applied to summing node 24. Node 24 produces an error value as a difference between the desired fuel injection quantity and the injected fuel quantity estimate and applies this error value to a controller 26. Controller 26 is responsive to the error value to determine a fuel command adjustment value, wherein the Initial fueling command and the fuel command adjustment value are applied to a second summing node 28. The output of summing node 28 is the output 30 of system 10 and represents a final fueling command that is the initial fueling command produced by table 14 adjusted by the fuel command adjustment value produced by controller 26.
While system 10 of FIG. 3 provides for a closed-loop fuel control system utilizing a virtual sensor to achieve at least some control over variations in injected fuel quantities, it has a number of drawbacks associated therewith. For example, a primary drawback is that prior art systems of the type illustrated in FIG. 3 are operable to compensate for variations in only a single operating parameter. Control over variations in additional parameters would require prohibitively large and difficult to manage multi-dimensional look-up tables, wherein such tables would be limited to only operating parameters capable of compensation via look-up table techniques. For operating parameters that deteriorate or change with time, for example, compensation via look-up tables simply does not work without some type of scheme for updating such tables to reflect changes in those operating parameters.
As another drawback of prior art systems of the type illustrated in FIG. 3, such systems are not closed-loop with respect to injector-to-injector fueling variations. For example, referring to FIG. 16, a plot 35 of measured fuel injection quantity vs. injector actuator commanded on-time (i.e., desired fueling command) for each injector (cylinder) of a six-cylinder engine, is shown wherein the between-cylinder fueling variations are the result of various mismatches in the fueling system hardware. As is apparent from plot 35, the between-cylinder fuel injection quantity variations are quite pronounced and generally unacceptable in terms of accurate fueling control. While known cylinder balancing techniques could reduce such cylinder-to-cylinder fueling variations, the fuel control system of FIG. 3 would be ineffective in reducing such variations. Moreover, the fuel control system of FIG. 3 would further be ineffective in reducing engine-to-engine fueling variations. Referring to FIG. 17, for example, plots of average injected fuel vs. injector on-time for three engine fueling extremes are illustrated. Nominal engine fueling requirements are illustrated by curve 36, minimum engine fueling conditions are illustrated by curve 38 and maximum engine fueling conditions are illustrated by curve 40. While engines of the same type may be designed for identical fueling requirements, their actual fueling requirements may fall anywhere between curves 38 and 40. Unfortunately, the prior art fuel control system of FIG. 3 cannot compensate for such engine-to engine fueling variations. In general, if such control parameter variations are not attributable to the operating parameter for which the system is designed to compensate for, but are instead attributable to other error sources for which the control system of FIG. 3 is not designed to compensate for, the system performance may actually be worse than would otherwise be the case with conventional fuel control techniques.
By the nature of their uses in a wide variety of applications, engines are typically required over their operating lifetimes to work in environments wherein many internal and external parameters that affect engine performance may vary, cannot be controlled and/or cannot be, or typically are not, measured. Heretofore, known control systems have attempted to improve injected fueling accuracy using a parameter that is both measurable and controllable. Such systems typically operate by making control changes, based on an estimated sensitivity in the fueling quantity, to this measurable and controllable parameter using assumed values for other internal and/or external parameters rather than taking into account performance effects and interactions of these other parameters. By contrast, if the injected fueling quantity can be estimated utilizing a sensor or virtual sensor that is independent of many of the internal and external parameters that affect the engine""s injected fueling quantity, a robust closed-loop fueling quantity control can be performed directly on the estimated fuel quantity rather than on only one of the control parameters that affect the fueling quantity. What is therefore needed is an improved strategy for adaptively estimating injected fuel quantities based on real-time performance of certain fuel system operating conditions throughout an injection event to thereby allow for robust and accurate operation as well as straightforward integration into complex fuel control systems. Ideally, such a strategy should be capable of minimizing between-cylinder and between-engine fueling variations.
The present invention may comprise one or more of the following features and combinations thereof. A system for estimating an auxiliary-injected fuel quantity injected into an internal combustion engine separate from a main-injected fuel quantity may comprise a fuel injector responsive to an injector on-time signal, having separate main-injection and auxiliary-injection on-times, to inject fuel into the engine, a fuel collection unit supplying fuel to the fuel injector, a fuel pump supplying pressurized fuel to the fuel collection unit, a pressure sensor in fluid communication with the fuel collection unit and producing a pressure signal indicative of fuel pressure therein, and a control circuit. The control circuit may periodically generate an auxiliary-injected fuel quantity model by disabling the fuel pump prior to fuel injection, and enabling the fuel pump to resume fuel pumping following fuel injection, by the fuel injector, determine based on the pressure signal a first pressure in the fuel collection unit after stabilization of the fuel pressure therein following disablement of the fuel pump and prior to the fuel injection, determine based on the pressure signal a second pressure in the fuel collection unit after the fuel injection and prior to resuming pumping of fuel by the fuel pump, and form the auxiliary-injected fuel quantity model as a function of the first and second pressures and the injector on-time signal for a number of different engine operating conditions. The control circuit may then estimate the auxiliary-injected fuel quantity according to the auxiliary-injected fuel quantity model.
The control circuit may be configured to estimate for each of the number of different engine operating conditions a total injected fuel quantity, corresponding to a sum of the main-injected fuel quantity and the auxiliary-injected fuel quantity, as a function of the first and second pressures and of the injector on-time signal, the main-injected fuel quantity according to a main-injected fuel quantity model, and an auxiliary-injected fuel quantity value as a difference between the total injected fuel quantity and the main-injected fuel quantity. The control circuit may form the auxiliary-injected fuel quantity model as a function of the auxiliary-injected fuel quantity values for each of the number of different engine operating conditions.
The auxiliary-injected fuel quantity may correspond to a post-injected fuel quantity injected into the engine following injection of the main-injected fuel quantity, the auxiliary-injected fuel quantity values may correspond to post-injected fuel quantity values, the auxiliary-injection on-time may correspond to a post-injection on-time, and the auxiliary-injected fuel quantity model may correspond to a post-injected fuel quantity model. In this embodiment, the injection on-time signal may further include a separate pilot-injection on-time for injecting a pilot-injected quantity of fuel into the engine prior to injection of the main-injected fuel quantity, and the control circuit may be configured to further disable for each of the number of engine operating conditions the pilot-injection on-time prior to the fuel injection, and enable the pilot-injection on-time following the fuel injection, by the fuel injector. In this embodiment, the control circuit may further be configured to determine a post-injected fuel quantity error as a difference between the post-injected fuel quantity and a commanded post-injected fuel quantity, and to adjust the post-injection on-time to minimize the post-injection fueling quantity error.
In an alternative embodiment, the auxiliary-injected fuel quantity may correspond to a pilot-injected fuel quantity injected into the engine prior injection of the main-injected fuel quantity, the auxiliary-injected fuel quantity values may correspond to pilot-injected fuel quantity values, the auxiliary-injection on-time may correspond to a pilot-injection on-time, and the auxiliary-injected fuel quantity model may correspond to a pilot-injected fuel quantity model. In this embodiment, the injection on-time signal may further include a separate post-injection on-time for injecting a post-injected quantity of fuel into the engine following injection of the main-injected fuel quantity, and the control circuit may be configured to further disable for each of the number of engine operating conditions the post-injection on-time prior to the fuel injection, and enable the post-injection on-time following the fuel injection, by the fuel injector. In this embodiment, the control circuit may further be configured to determine a pilot-injected fuel quantity error as a difference between the pilot-injected fuel quantity and a commanded pilot-injected fuel quantity, and to adjust the pilot-injection on-time to minimize the pilot-injection fueling quantity error.
In any of the embodiments, the control circuit may be configured to estimate a control flow leakage value as a function of the first and second pressures and of the injector on-time signal, and to estimate the total injected fuel quantity further as a function of the control flow leakage value. The system may further include means for determining an operating temperature of the engine and producing an engine temperature signal corresponding thereto, and the control circuit may be configured to estimate a parasitic flow leakage value as a function of the first and second pressures and of the engine temperature signal, and to estimate the total injected fuel quantity further as a function of the parasitic flow leakage value. The means for determining an operating temperature of the engine may be a temperature sensor producing a fuel temperature signal indicative of a temperature of the pressurized fuel, and the engine temperature signal in the estimate of the parasitic flow leakage value may thus correspond to the fuel temperature signal. The means for determining an operating temperature of the engine may alternatively be a temperature sensor producing a coolant temperature signal indicative of a temperature of engine coolant fluid, and the engine temperature signal in the estimate of the parasitic flow leakage value may thus correspond to the coolant temperature signal. The control circuit may be responsive to the pressure signal to estimate a bulk modulus of the pressurized fuel, and the control circuit may be configured to estimate the total injected fuel quantity further as a function of the bulk modulus of the pressurized fuel.
In any of the embodiments, the control circuit may be configured to generate the main-injected fuel quantity model by periodically disabling the fuel pump and the corresponding post- or pilot-injection on-time prior to fuel injection, and enabling the fuel pump to resume pumping and the corresponding post- or pilot-injection on-time following fuel injection, by the fuel injector, determining based on the pressure signal a third pressure in the fuel collection unit after stabilization of the fuel pressure therein following disablement of the fuel pump and prior to fuel injection by the fuel injector, determining based on the pressure signal a fourth pressure in the fuel collection unit after fuel injection by the fuel injector and prior to resuming pumping of fuel by the fuel pump, and forming the main-injected fuel quantity model as a function of the third and fourth pressures and of the injector on-time signal for a plurality of different engine operating conditions. The control circuit may be configured to estimate for each of the plurality of different engine operating conditions a main-injected fuel quantity value as a function of the third and fourth pressures and of the injector on-time signal, and to form the main-injected fuel quantity model as a function of the main-injected fuel quantity values for each of the plurality of different engine operating conditions. The control circuit may be configured to estimate for each of the plurality of different engine operating conditions a control flow leakage value as a function of corresponding ones of the third and fourth pressures and injector on-time signals, and to estimate each of the plurality of main-injected fuel quantity values further as a function of a corresponding one of the plurality of control flow leakage values. The system may further include means for determining an operating temperature of the engine and producing an engine temperature signal corresponding thereto, wherein the control circuit may be configured to estimate for each of the plurality of different engine operating condition values a parasitic flow leakage value as a function of corresponding ones of the third and fourth pressures and of the engine temperature signal, and to estimate each of the plurality of main-injected fuel quantity values further as a function of a corresponding one of the parasitic flow leakage value. In one embodiment, the means for determining an operating temperature of the engine may be a temperature sensor producing a fuel temperature signal indicative of a temperature of the pressurized fuel, and the engine temperature signal in each of the plurality of estimates of the parasitic flow leakage value may then correspond to the fuel temperature signal. The means for determining an operating temperature of the engine may alternatively be a temperature sensor producing a coolant temperature signal indicative of a temperature of engine coolant fluid, wherein the engine temperature signal in each of the plurality of estimates of the parasitic flow leakage value may then correspond to the coolant temperature signal. The control circuit may be responsive to the pressure signal to estimate a bulk modulus of the pressurized fuel, and the control circuit may be configured to estimate for each of the plurality of different engine operating conditions the main-injected fuel quantity value further as a function of the bulk modulus of the pressurized fuel.
A system for minimizing post-injected fueling variations in an internal combustion engine may comprise a number of fuel injectors each responsive to one of a corresponding number of injector on-time signals to supply fuel to the engine, each of the injector on-time signals having separate main-injection and post-injection on-times, a fuel collection unit supplying fuel to each of the number of fuel injectors, a fuel pump supplying pressurized fuel to the fuel collection unit, a pressure sensor in fluid communication with the fuel collection unit and producing a pressure signal indicative of fuel pressure therein, and a control circuit. The control circuit may be configured to periodically disable the fuel pump prior to fuel injection, and enable the fuel pump to resume fuel pumping following fuel injection, by a selected one of the number of fuel injectors. The control circuit may be responsive to the pressure signal to determine a first pressure in the fuel collection unit after stabilization of the fuel pressure therein following disablement of the fuel pump and prior to fuel injection by the selected one of the number of fuel injectors, and to determine a second pressure in the fuel collection unit after fuel injection by the selected one of the number of fuel injectors and prior to resuming pumping of fuel by the fuel pump, and to periodically determine the first and second pressures for remaining ones of the number of fuel injectors. The control circuit may be configured to adjust one or more of the post-injection on-times as a function of the first and second pressures for each of the number of fuel injectors to minimize post-injection fueling variations between the number of fuel injectors.
The control circuit may be configured to determine for each of the number of fuel injectors a pressure difference value as a difference between corresponding ones of the first and second pressures, and to minimize post-injection fueling variations between the number of fuel injectors by adjusting the one or more of the post-injection on-times to minimize differences between the number of pressure difference values.
The control circuit may alternatively be configured to estimate for each of the number of fuel injectors a total injected fuel quantity as a function of corresponding ones of the first and second pressures, and a post-injected fuel quantity as a difference between the total injected fuel quantity and of a corresponding one of a number of commanded main fuel injection quantities, and to minimize post-injection fueling variations between the number of fuel injectors by adjusting the one or more of the post-injection on-times to minimize differences between the number of post-injected fuel quantities. The control circuit may be configured to estimate for each of the number of fuel injectors a control flow leakage value as a function of corresponding ones of the first and second pressures and of corresponding ones of the number of injector on-time signals, and to estimate for each of the number of fuel injectors the total injected fuel quantity further as a function of a corresponding one of the control flow leakage values. The system may further include means for determining an operating temperature of the engine and producing an engine temperature signal corresponding thereto, and the control circuit may be configured to estimate for each of the number of fuel injectors a parasitic flow leakage value as a function of corresponding ones of the first and second pressures and of the engine temperature signal, and to estimate for each of the number of fuel injectors the total injected fuel quantity further as a function of a corresponding one of the parasitic flow leakage values. In one embodiment, the means for determining an operating temperature of the engine may be a temperature sensor producing a fuel temperature signal indicative of a temperature of the pressurized fuel, and the engine temperature signal in the estimates of each of the number of parasitic flow leakage values may then correspond to the fuel temperature signal. The means for determining an operating temperature of the engine may alternatively be a temperature sensor producing a coolant temperature signal indicative of a temperature of engine coolant fluid, and the engine temperature signal in the estimates of each of the number of parasitic flow leakage values may then correspond to the coolant temperature signal. The control circuit may be responsive to the pressure signal to estimate a bulk modulus of the pressurized fuel, and to estimate each of the number of total injected fuel quantities further as a function of the bulk modulus of the pressurized fuel.
These and other objects of the present invention will become more apparent from the following description of the illustrative embodiments.